Line-drawing interpretation: bilateral symmetry

Results previously derived by the author are used to investigate the implication of bilateral symmetry in line drawings. It is shown that the line drawing of an orthographically protected surface of revolution exhibits bilateral symmetry about the projection of its axis of revolution irrespective of the viewing direction. Barring one exception, a bilaterally symmetric line drawing is necessarily the orthographic projection of a local surface of revolution whenever its symmetry axis continues to be the projection of a fixed line in space under perturbation of viewpoint; the axis of revolution is the invariant preimage of the symmetry axis. Various line-drawing causes are detailed which facilitate the deduction of invariant preimages of symmetry axes, and consequently of local surfaces of revolution     

Representing oriented piecewise C2 surfaces

To reason about shape, one must first represent it. We deseribe a representation scheme for a large class of surfaces. Our primary focus is the formalism; implementation issues receive little attention. A good representation must be more than just minimally sufficient for the task; it must also be unambiguous, stable, local, and convenient. We first discuss four well-known schemes in view of these requirements, and then turn to differential geometric representations and argue that they, in general, are inadequate by themselves. Practicability and robustness require the incorporation of global geometric information. As representation on the Gaussian sphere offers considerable convenience, it is proposed that surfaces be represented by their Gaussian images, associating with each point the value of its support function, that is, the signed distance of the oriented tangent plane at its preimage from the origin. Such a representation is locally generative. Consequently, it is unambiguous; it is unique up to the orientation and position of the represented surface. It is local in directions of nonzero surface curvature. Also, it is additive; hence, although it is not stable, this problem seems circumventable. Several examples are provided.     

Aromatic polyureas: a new class of nonlinear optical polymer with large second-harmonic generation

The second-order nonlinear optical properties of aromatic polyureas are reported. From Maker fringe measurements, the nonlinear d/sub 33/ coefficient of poled polyurea films with and without pendant chromophores was found to be 20*10/sup -9/ esu and 12*10/sup -9/ esu, respectively, at 1.064 mu m. Aromatic polyurea having no pendant chromophores shows a cutoff wavelength of transmission at 307 nm which is the first example of organic NLO materials to be optically transparent at such low wavelengths.<>     

The effect of central metal atom on the electrical properties of phthalocyanine macromolecule

In order to investigate the effect of the central metal atom variation on the electrical properties of phthalocyanine macromolecule, iron, cobalt, nickel and copper as the di-valent metals were incorporated into the macrocycle. The electrical properties of these metallophthalocyanines were then studied to establish a structure-property relation-ship. The experimental data show that electrical parameters are greatly influenced by the choice of metal atom. It remains to be investigated whether results are dominantly interpretable in terms of the size of the metal, intermolecular π-electron delocalization of the macrocycle, or other molecular orbital property.     

Nanotechnology and health safety--toxicity and risk assessments of nanostructured materials on human health

The field of nanotechnology has recently emerged as the most commercially viable technology of this century because of its wide-ranging applications in our daily lives. Man-made nanostructured materials such as fullerenes, nanoparticles, nanopowders, nanotubes, nanowires, nanorods, nanofibers, quantum dots, dendrimers, nanoclusters, nanocrystals, and nanocomposites are globally produced in large quantities due to their wide potential applications, e.g., in skincare and consumer products, healthcare, electronics, photonics, biotechnology, engineering products, pharmaceuticals, drug delivery, and agriculture. Human exposure to these nanostructured materials is inevitable, as they can enter the body through the lungs or other organs via food, drink, and medicine and affect different organs and tissues such as the brain, liver, kidney, heart, colon, spleen, bone, blood, etc., and may cause cytotoxic effects, e.g., deformation and inhibition of cell growth leading to various diseases in humans and animals. Since a very wide variety of nanostructured materials exits, their interactions with biological systems and toxicity largely depend upon their properties, such as size, concentration, solubility, chemical and biological properties, and stability. The toxicity of nanostructured materials could be reduced by chemical approaches such by surface treatment, functionalization, and composite formation. This review summarizes the sources of various nanostructured materials and their human exposure, biocompatibility in relation to potential toxicological effects, risk assessment, and safety evaluation on human and animal health as well as on the environment.     

Line-drawing interpretation: straight lines and conic sections

Line drawings of man-made scenes often exhibit instances of straight lines and conic sections, i.e. ellipses, parabolas, and hyperbolas. Constraints imposed on the scene by such instances are investigated, under the assumption of general viewpoint, i.e. the mapping of the viewed surface onto the line drawing is stable under perturbation of the viewpoint within some open set. Both orthographic and perspective projection are considered. The viewed surfaces are assumed to be piecewise C³. It is shown that straight lines and conic sections in line drawings are projections of scene edges which are also straight lines and conic sections, respectively. It is also shown that scene events which project onto straight lines or conic sections cannot be combinations of view-point-independent and viewpoint-dependent edges. Further, continuous-surface-normal depth discontinuities which project onto straight lines can be locally described by developable surfaces, and those which project onto conic sections can be locally described by nondevelopable quadric surfaces. Each of these quadric surfaces is determined up to four degrees-of-freedom by its projection     

Line-drawing interpretation: A mathematical framework

We report progress toward a mathematical theory of line-drawing interpretation. A working framework is developed, and a variety of tools and techniques are demonstrated within it. We begin with a concise review of related work. Then, we detail our assumptions—the imaging geometry is well approximated by orthographic or perspective projection, the viewpoint is general, the world is composed of piecewise C³ surfaces, and continuous-surface-normal depth discontinuities are the only viewpoint-dependent edges. This is followed by the presentation of a projective mapping which we expect will find considerable use in the extension of results derived for orthographic projection to perspective projection. Next, Whitney's definition of an excellent mapping is reviewed and it is shown that both orthographic and perspective projections of piecewise C³ surfaces are excellent under general viewpoint. It is thus demonstrated that there are basically only two different types of local singularities—folds and cusps—associated with the projection of a C³ surface. The loci of the singular values are C³ curves in the line drawing, except for cusps at their nonjunction terminations. All previous work based on Whitney's results on excellent mappings has needed to assume stability under perturbation of the viewed surface. This assumption, which is unverifiable by a remote observer, is rendered unnecessary by our results. After characterizing viewpoint-dependent edges as folds and cusps, we turn our attention to the modes of interaction between viewpoint-independent and viewpoint-dependent edges. It is shown that only isolated points on viewpoint-dependent edges may lie on surface-patch boundaries, and that viewpoint-independent and viewpoint-dependent edges are always cotangent at their nonocclusion junctions in line drawings, but have different curvatures. Finally, we investigate continuity constraints imposed on the scene by its line drawing. We show that a viewpoint-independent edge in a line drawing is C³ if and only if the edge is C³ in space, and that a viewpoint-dependent edge in a line drawing is C³ if and only if the surface on which it lies in space is C³ along the edge.This work was supported in part by the Defense Advanced Research Projects Agency under Contract N00039-84-C-0211.     

Chemical synthesis of processible electrically conducting poly(3-dodecylthiophene)

The chemical synthesis of poly(3-dodecylthiophene) is reported. The polymer was characterized by ¹H-NMR, IR and UV absorption spectroscopic techniques. The room temperature electron spin resonance spectrum yielded a g value of 2.0091 and a linewidth of 6.60 Gauss. The solution cast polymer films after doping with iodine exhibited an electrical conductivity of 12 S/cm.